Wireless or "mobile" communications have been found to be of great value to station users who roam large geographic areas yet who desire immediate access to telephone services, especially in critical situations. Presently, the most common form of personal wireless communications are cellular telephones. Cellular telephones are, of course, operable in cooperation with known cellular networks which consist of four basic components: a Mobile Telephone Switching Center (MTSC), a cell site containing a controller and radio transceiver, system interconnections, and mobile or portable telephone units.
The MTSC is known to those skilled in the art as a digital telephone exchange which controls the switching between the Public Switched Telephone Network (PSTN) and the cell sites for all wireline-to-mobile and mobile-to-wireline calls as well as for mobile-to-mobile calls. The MTSC also processes mobile unit status data received from the cell site controllers, switches calls to other cells, processes diagnostic information, and compiles billing statistics.
In operation, when the MTSC receives a call for a mobile telephone user from the Public Switched Telephone Network, it deciphers the telephone number dialed by the wireline user and alerts the controllers at the cell sites to page the corresponding mobile unit. When a mobile telephone user places a call, the MTSC accepts the dialing data from the cell site controller and dials the desired number.
As referenced above, typical cellular networks include multiple adjoining cells each of which contains at least one cell site controller which operates under the direction of the MTSC. The cell site controller manages each of the radio channels at the site, supervises calls, turns the radio transmitter and receivers on and off, injects data onto the control and user channels, and performs diagnostic tests on the cell site equipment. Each cell contains one radio transmitter and two radio receivers. As those skilled in the art will further recognize, in operation both receivers are typically tuned to the same frequency, but the one receiving the stronger radio signal is continuously selected.
Each cell further has at least one radio channel that transmits control data to and receives control data from the mobile units. This control data tells the mobile unit that a call is coming from the MTSC or, conversely, tells the controller that a mobile telephone user wishes to place a call. To complete the connection, the controller uses the control channel to tell the mobile unit which user channel has been assigned to the call.
While cellular networks have been found to be of great value to mobile users whose travels span many miles, they have also been found to be prohibitively expensive to implement for small scale applications wherein system subscribers only desire wireless telephone services in a limited geographic area, such as, for example, within office buildings or in a campus environment.
The Personal Communications Network (PCN) is a relatively new concept in mobile communications developed specifically to serve the aforementioned applications. Like cellular telephony, a Personal Communications Network relates telephone numbers to persons rather than fixed locations. Unlike cellular telephones, however, the PCN phones are directed to small geographic areas thus defining "microcellular" areas designed to operate in similar to fashion to large scale cellular telephone networks. PCN technologies are also similar to residential cordless telephones in that both utilize base stations and wireless handsets. Unlike the former, however, PCN technology utilizes advanced digital communications features which may be implemented either as private networks or regulated services. When offered by communications carriers as services, this PCN capability is generally referred to as Personal Communications Services (PCS).
Microcellular Personal Communications Services (PCS) are expected to provide wireless access for an increasingly important segment of the communications market. Such PCS services therefore must meet the needs of the consumer market where expectations for good speech reproduction, immediate availability, low congestion, seamless handoff of all calls, and universal access are demanding.
There are presently in existence non-cellular, wireless PCN systems which require the design and implementation of complete overlaying networks to achieve the above-mentioned desired telephone services. See, for example, U.S. Pat. No. 4,980,907 issued to Raith et al and assigned to Telefonaktiebolaget L M Ericsson. This approach of providing a substantially new overlay of network components is, of course, highly expensive to implement and undesirable from a Local Exchange Carrier (LEC) perspective.
Consequently, a need has developed to provide a system and method for providing microcellular Personal Communications Services (PCS) which utilizes existing wireline switches for PCS deployment. More particularly, a need has developed to provide a Distributed Radio Port Controller (D-RPC) architecture which supports such a PCS system with minimal impact on the existing embedded base of switches. A need has further developed to provide a method for controlling call processing in such a system so as to properly effect the routing of the voice channels when a call origination, call delivery, intra-RPC automatic link transfer (ALT) or inter-RPC ALT is needed.